Technical Field
The present disclosure relates to electrosurgical systems and methods for performing electrosurgery. More particularly, the present disclosure relates to controlling the delivery of power to tissue during the cook stage of a tissue sealing procedure.
Description of Related Art
Electrosurgery involves application of high radio frequency (RF) electrical current to a surgical site to seal, cut, ablate, or coagulate tissue. In monopolar electrosurgery, a source or active electrode delivers RF energy from the electrosurgical generator to the tissue and a return electrode (e.g., a return pad) carries the current back to the generator. In monopolar electrosurgery, the active electrode is typically part of the surgical instrument held by the surgeon and applied to the tissue to be treated. The patient return electrode is placed remotely from the active electrode to carry the current back to the generator.
In bipolar electrosurgery, one of the electrodes of the hand-held instrument functions as the active electrode and the other as the return electrode. The return electrode is placed in close proximity to the active electrode such that an electrical circuit is formed between the two electrodes (e.g., electrosurgical forceps). In this manner, the applied electrical current is limited to the body tissue positioned between the electrodes. When the electrodes are sufficiently separated from one another, the electrical circuit is open and thus inadvertent contact of body tissue with either of the separated electrodes does not cause current to flow.
Bipolar electrosurgery generally involves the use of forceps. A forceps is a pliers-like instrument which relies on mechanical action between its jaws to grasp, clamp and constrict vessels or tissue. So-called “open forceps” are commonly used in open surgical procedures whereas “endoscopic forceps” or “laparoscopic forceps” are, as the name implies, used for less invasive endoscopic surgical procedures. Electrosurgical forceps (open or endoscopic) utilize mechanical clamping action and electrical energy to affect hemostasis on the clamped tissue. The forceps include electrosurgical conductive plates which apply electrosurgical energy to the clamped tissue. By controlling the intensity, frequency and duration of the electrosurgical energy applied through the conductive plates to the tissue, the surgeon can coagulate, cauterize and/or seal tissue.
Tissue or vessel sealing is a process of liquefying the collagen, elastin, and ground substances in the tissue so that they reform into a fused mass with significantly-reduced demarcation between the opposing tissue structures. Cauterization involves the use of heat to destroy tissue and coagulation is a process of desiccating tissue wherein the tissue cells are ruptured and dried.
Tissue sealing procedures involve more than simply cauterizing or coagulating tissue to create an effective seal; the procedures involve precise control of a variety of factors. For example, in order to affect a proper seal in vessels or tissue, two predominant mechanical parameters must be accurately controlled: the pressure applied to the tissue and the gap distance between the electrodes (i.e., the distance between opposing jaw members or opposing sealing plates). In addition, electrosurgical energy must be applied to the tissue under controlled conditions to ensure the creation of an effective vessel seal. Techniques have been developed to control or vary the power of energy applied to the tissue during the tissue sealing process. When a target tissue impedance threshold is reached, the tissue seal is deemed completed and the delivery of electrosurgical energy is halted.
The power control systems of conventional electrosurgical generators include nonlinearities that may impact the quality and consistency of tissue seals. To overcome these nonlinearities, electrosurgical generators have been designed to include high performance control systems. These high performance control systems use field-programmable gate array (FPGAs) technology to allow for increased generator control speeds so that the high performance control systems can overcome the nonlinearities of conventional power control systems.